Electrode system for rectifying or controlling high or intermediate frequency oscillations



2,161,600 HIGH June 6, 1939.

ELECTRODE Patented June 6, 1939 Willem Christiaan van Gee], Eindhoven, Nether lands, assignor to N. V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands, a corporation of the Netherlands Application June 20, 1936, Serial No. 86,288

In Germany July 30, 1935 v 6 Claims. (Cl.- 175-366) UNITED STATES PATENT OFFICE ing electrode is applied. It may be advantageous to provide this insulating coating separately.

.Such an electrode system has various advantages when used, for instance,-in radio receiving or television apparatus. A rectifying effect of the system when used as a detector can be readily obtained by means of va comparatively low voltage applied to the electrodes, this voltage on account of the said very small thickness of the insulating coating being capable of setting up an electric field of considerable intensity between the electrodes.

However, such an electrode systemfor rectifying or controlling high or intermediate'frequency oscillations has the drawback thatit is possessed of a comparatively high self-capacity.

This capacity depends either on the size of the contact surface between the well conducting electrode and the insulating coating, or on the size of the contact surface between the semi-conductive electrode and the insulating coatin or again on the size of the contact surface between the semi-conductive electrode ,and the supply conductor, for in the latter case substantially only that column of the semi-conductive electrode, whose section substantially corresponds to one of the systemparts determining the capacity. of the system in such 'a-imanner by means .of a mass in the iiquid state,.fthat the c'Qnta-cts'urface determining the capacity s reduced to a: surface not exceeding l mnififeithera by' he surface tension .of the mass: applied in, 'xact small quantity, or byjan envelo'p'e arranged about.'said' mass on theicontact ace. uid :mass may either consist @91 t molten rode mat compound in ther adi'ssolyed or suspended state.

crystal acting as a detector in a radio receiving set. A crystal detector exhibits a rectifying effect only at one or some points of the crystal surface and more particularly where an insulating coating is available on the surface which coating must have such a thickness that its resistance does not have an excessive value and corresponds to the applied voltage to be rectified. Thus, when using a crystal as adetector the crystal surface must be scanned with the aid of a pointed metal contact until a'point possessing a rectifying effect has been found.

This drawback is not inherent to electrode systems according to the present invention. In these systems any point of the insulating coating has a rectifying effect, if on either side of the' insulating coating there is a point of one terminal electrode that lies, opposite a point of the other terminalelectrode. m. .Sincethe thickness of the insulating coating in an electrode system according to thezirivent'ion is determined beforehand and the whole contact surface has a detector effect, the capacity may:

be arbitrarily chosen.

The same holds good when the electrode system very difficult to obtain a small surface capable of being reproduced with such a graphite layer.

The present invention permits the self-capacity of an electrode system or cell to be 'made=extremely low. -However, in contra-distinction to the prior art, by reason of the means used according to the invention for obtaining the desired effect, it is possible to determine beforehand the definite valueof the self-capacity of {the cellwhich is capable of being'reproduced. In 'viewof the factthat the self-capacity has a definite influence on a circuit comprising the cell it is of ,great i'mportance that the self-capacity 'themselvesfif I v cult would lacedby" 'another one; -"I'he el ec'trodefls tem according to the inven- ;cf such cells has the, same value and is capable i of being reproduced; fIn' order to ensure the most a -favo'rab1e;operation, in such a circuit certain -measure's, are taken when designing it. If the self-capacityof.;;the cell wouldbe' different, then.

" tam-measures have e ares-"could not bring out itia cell adapted to the cir-v due to the disturbing effect exerted, for instance,

on the high frequency part, the source of alternating current heating power cannot be provided at optional points in such receivers.

These supply conductors being obviated, the problem of the arrangement of a detector according to the invention is greatly simplified, since it may be provided where it is most suitable in view of the smallest length of the connecting wires. Owing to its small size and weight such a system may be suspended and mounted in the wiring itself.

The invention will be more clearly understood by reference to the accompanying drawing wherein Figs. 1, 2 and 3 illustrate enlarged views of various modifications of the electrode systems according to the present invention.

For the semi-conductive (electro-negative) electrode I (Figure 1) cuprous sulphidc- (Ours) is used, which is applied as such on a brass sup-' port 2 by pressing. After that the semiconductor is coated with an insulating polystyrene coating 3 which may be effected by immersing it in a bath containing insulating coating material dissolved in benzene and by slowly drawing it out of this bath. In accordance with the voltage to be blocked a thickness of 1 to 10;; may be used.

On the insulating coating is placed a tube 4 of quartz whose bore extends conically towards the bottom side so that the aperture 5 is about 0.125 mm This tube perfectly adheres tothe insulating coating 3 when the material of the insulating coating itself is used as an adhesive. In this case heating up to more than 100 0., for instance, may be necessary. The supply conductor 6 is inserted into this tube and after that the tube 4 is filled with a metal suspension 1 such as a sus pension of platinum in alcohol, or with a colloidal graphite solution (for instance, the colloidal graphite solution in water sold under the registered trade-mark Aquadag).

agent thegood conductive electrode I which is constituted by the solid residue is connected both mechanically and electrically to the supply conductor 6. Instead of a metal suspension it is also possible to use a solution of a chemical compound of a metal, the chemical compound being reduced. It is possible, for instance, to use one of the well known silver solutions such as an ammoniacal silver solution to which glucose is added.

If desired, the tube I may be removed after the good conductive electrode has been formed.

The following method of manufacture concerns a detector (Figure 2) wherein the negative electrode consists of selenium.

A definite quantity of the liquid selenium 9 is applied on to a brass plate 8 and after cooling down it is covered with an insulating coating ID of artificial resin which covers also the brass side where the selenium is provided as appears from the drawing.

After concentration' by evaporation of the suspension The support together with the selenium and the insulating coating provided thereon is introduced into a furnace and heated for some time (generally 2 to 24 hours) at a temperature of about 200 C. This operation has for its purpose to convert the selenium into the conductive crystalline modification. When the synthetic resin used for the coating layer is polystyrene then heating has the additional advantage that the polystyrene can be polymerised thoroughly, thus improving the favorable dielectric properties.

On to the insulating coating a definite quantity of Rose metal ll (50 Bi, 27.1 Pb, 22.9 Sn) is applied which is arranged at the level of the spherical selenium part 9. The metal II will contact with the insulating coating over a limited surface only (for instance 0.25 mmfi). This surface can be previously determined and depends on the surface tension and the quantity of material.

While the drop II is still in liquid form a supply conductor [2 is immersed which after so lidification of the electrode material ensures a perfect mechanical and electrical joint.

Both the above examples relate to the manufacture of electrode systems wherein the semiconductive electrode is applied in the form of a thin layer on to a flat plate, whereas the good conductive electrode is formed inside an envelope or as a definite drop. Hereinafter the manufacture of a system according to the invention will be set out by reference to Figure 3, in

which the selenium, i. e., the semi-conductive electrode is provided in a pearl-shaped envelope.

Graphite H is provided in a steatite pearl I3 having a cylindrical bore of about 0.5 mm. up to a distance of about 0.03 mm. from the upper edge. This graphite assures a perfect contact with the selenium [5 to be applied thereon. At It the graphite is electrolytically coppered in Order that a supply conductor can be soldered thereto.

After that the cavity of the pearl above the graphite is filled with liquid selenium IS. A smooth surface and a uniform thickness of the layer can be obtained by striking, for instance, a razor over the selenium while it is in the liquid state.

Thereupon an insulating coating I1 is formed on the selenium and, if desired, on the whole surface of the pearl, by immersion into a solution of polystyrene in benzene. After this treatment the assembly is heated at about 200 C. as has been set out in the last-mentioned example.

The counterelectrode l8 provided on the insulating coating I1 is constituted by a definite metal quantity having a low melting point such as Woods metal (50 Bi, 25 Pb, 12.5 Sn, 12.5 Cd),

in which the conductor [9 is inserted, while the drop is in liquid form,-so that the conductor is secured upon solidification.

In order to render the assembly more rigid and to secure the supply conductors mechanically in a suitable manner such an electrode system, if required after having been inserted in-a tube, is filled up with compound mass. In this manner the supply conductors bear in the compound mass so that the connecting points of the electrodes are not liable to mechanical stresses.

Also other methods of manufacturing elec-' trode systems fall within the scope of the invention as defined by the appended claims.

What I claim is:

1. An electrode system for rectifying or controlling high or intermediate frequency electrical oscillations, comprising an electro-positive electrode of an alloy composed of at least bismuth, lead and tin and an electro-negative electrode of selenium, an insulating coating 'of polystyrene provided between the electrodes, and characterised in that at least one of the capacity determining parts of the system is formed with the aid of a mass in the liquid state in-"such a manner that the contact surface determining the electro-.

static capacitance is limited to a surface not exceding 10 mm..

2. An electrode system as claimed in claim 1, in which the portion yielding the surface determining the capacity is applied in the molten state.

3. An electrode system comprising a pair of main electrodes, one of which is electro-positive and is made of an alloy composed of at least bismuth, lead and tin, and the other of which is electro-negative and is made of selenium, and a thin insulating layer of polystyrene interposed between and contacting the surfaces of the main 7 electrodes. a

4. An electrode system according to claim 3 wherein the electro-positive electrode is made of Rose metal.

5. An electrode system according to claim 3 wherein the electro-positive electrode is made of Woods metal.

of the cylinder and the selenium electrode, a

quantity of Woods metal constituting the positive electrode of the system contacting with the polystyrene layer on the side opposite to the negative electrode, and a lead connected to each of the electrodes.

WILLEM CHRIB'I'IAAN vnt am. 

